In a conventional railway truck of the four-wheel type, the truck geometry is such that the axles are constrained by the sideframes and bearing adapters to remain substantially parallel to each other under most conditions of operations. It is generally desirable that a ninety degree, or right angular relationship be maintained between the axled wheelsets and the sideframes during travel on straight and curved track.
If there are small differences in the longitudinal dimensional tolerances of the sideframe pair wheelbases, or if there are track inputs which cause angular movement between the bearing, the bearing adaptor, and the sideframe, or longitudinal movement of the bearing adapter within the sideframe pedestal jaw, an unsquare condition known as lozenging will occur. Lozenging is where the sideframes operationally remain parallel to each other, but one sideframe moves slightly ahead of the other in a cyclic fashion; this condition is also known as parallelogramming or warping. Warping causes wheel misalignment with respect to the track; it is more pronounced on curved track and usually provides the opportunity for a large angle-of-attack to occur, as will be explained shortly. Ideally, it is desirable if the axles could align themselves with the radial axis of the tracks, as with the "steerable" type of trucks, where no angle-of-attack occurs. See FIG. 3A. However, with non-steerable trucks, this does not occur and the tracks work against the wheeled axles, forcing them to cause the truck to assume an out-of-square or warped condition. An out-of-square truck travelling through curved track results with a large angle of attack, defined herein as .theta., the angle between the wheel flanges and the wheel rails. See FIG. 3B. A good compromise between a steerable truck and one which is easily warped, is a truck which will remain square (unwarped), resulting with a low angle of attack and a higher threshold speed at which truck hunting will occur, like the one of FIG. 3C. Past research efforts have noted a significant relationship between truck warping and resultant truck hunting.
Truck hunting is a continuous wheel set instability where the truck weaves down the track in an oscillatory fashion, usually with the wheel flanges striking against the rail, creating wheel drag. Surprisingly, this means that drag can occur even on straight track. Under truck hunting and dragging conditions, a substantial amount of frictional wear occurs between the wheel and track, wasting a great deal of locomotive horsepower and fuel in overcoming the friction forces. These conditions can also cause lading damage to vibration sensitive ladings, such as automobiles.
To improve curving associated with truck warping, prior art structures interposed elastomeric devices between the bearing adapter and the sideframe as a means for maintaining the wheelsets and sideframes in a generally right angular relationship with respect to each other while traveling on straight track. These devices were said to significantly reduce truck misalignment by providing a sufficiently resistive shear stiffness against lateral sideframe impacts, thereby assisting or maintaining the right angular relationship between the sideframes and wheelsets. Generally, it was recognized as being undesirable to transmit any source of perturbation through the axle, sideframe, and bolster, and these types of prior art devices intended to accomplish a damping of the disturbances rather than suppressing their initiation. A sideframe structure incorporating this type of prior art device is shown in U.S. Pat. No. 4,674,412, which is assigned to AMSTED Industries, Inc. of Chicago, Ill., the assignee of the present disclosure. Although this device helped prevent truck lozenging in curves, the truck warp stiffness remained unchanged.
Adding positioning lugs to each of the sideframe pedestal jaws as a means for preventing possible lozenging problems on a newly assembled truck was the subject of currently-pending application Ser. No. 180,026, filed on Jan. 11, 1994, and commonly owned by the assignee of this disclosure. The positioning lugs correct built-in lozenging which results from wheelbase dimensional tolerances, although they do not fully eliminate bearing adapter movement within the pedestal jaw.